Wave Force on a Partially Submerged Fixed Horizontal Circular Cylinder

2018 ◽  
Author(s):  
Monica C. Silva ◽  
Marcelo A. Vitola ◽  
Paulo de Tarso T. Esperança ◽  
Sergio H. Sphaier
Keyword(s):  
Experimental Data ◽  
Free Surface ◽  
Circular Cylinder ◽  
Wave Force ◽  
Offshore Wind ◽  
Circular Cylinders ◽  
Wave Flow ◽  
Energy Devices ◽  
Floating Offshore Wind Turbines ◽  
Horizontal Circular Cylinder

Circular cylinders are one of the most common geometries used in many structures, such as fixed platforms, risers, umbilical cables, offshore fish farms, floating offshore wind turbines, wave energy devices, plastic cleanup booms, and oil containment booms. Although partially submerged horizontal circular cylinders can be found in many offshore and marine structures, few works have investigated the influence of their positions beneath the free surface and the resulting wave force. The present work aimed to numerically study the wave force acting on a fixed horizontal circular cylinder near the free surface for different depths. The wave flow was modeled using a viscous model available in the StarCCM+ software using a two-dimensional numerical wave tank. The governing equations were solved using the finite volume in an unstructured mesh. A circular cylinder with a diameter (D) of 0.10 m and a regular wave with a steepness (H/L) of 0.025 were used in the present study. In this case, the cylinder diameter is much smaller than the wave length. Three different submerged depths were investigated, and the numerical results were compared with experimental data extracted from Dixon [1]. Good agreement was found for the first two cylinder positions (zc/D = 0 and −0.3). For the last case (zc/D = −0.5), a phase shift was observed. However, by correcting it, the agreement between the numerical and experimental data was also good.

Software-in-the-Loop Combined Machine Learning for Dynamic Responses Analysis of Floating Offshore Wind Turbines

2021 ◽  
Author(s):  
Peng Chen ◽  
Changhong Hu ◽  
Zhiqiang Hu
Keyword(s):  
Machine Learning ◽  
Experimental Data ◽  
Wind Turbines ◽  
Dynamic Responses ◽  
Offshore Wind ◽  
Learning Technology ◽  
Mean Values ◽  
Offshore Wind Turbines ◽  
Floating Offshore Wind Turbines ◽  
Brute Force Method

Abstract Artificial intelligence (AI) brings a new solution to overcome the challenges of Floating offshore wind turbines (FOWTs) to better predict the dynamic responses with intelligent strategies. A new AI-based software-in-the-loop method, named SADA is introduced in this paper for the prediction of dynamic responses of FOWTs, which is proposed based on an in-house programme DARwind. DARwind is a coupled aero-hydro-servo-elastic in-house program for FOWTs, and a reinforcement learning method with exhaust algorithm and deep deterministic policy gradient (DDPG) are embedded in DARwind as an AI module. Firstly, the methodology is introduced with the selection of Key Disciplinary Parameters (KDPs). Secondly, Brute-force Method and DDPG algorithms are adopted to changes the KDPs’ values according to the feedback of 6DOF motions of Hywind Spar-type platform through comparing the DARwind simulation results and those of basin experimental data. Therefore, many other dynamic responses that cannot be measured in basin experiment can be predicted in good accuracy with SADA method. Finally, the case study of SADA method was conducted and the results demonstrated that the mean values of the platform’s motions can be predicted with higher accuracy. This proposed SADA method takes advantage of numerical-experimental method, basin experimental data and the machine learning technology, which brings a new and promising solution for overcoming the handicap impeding direct use of conventional basin experimental way to analyze FOWT’s dynamic responses during the design phase.

Numerical Modelling of Breaking Wave Interaction With a Group of Four Vertical Slender Cylinders in Square Arrangements

2016 ◽  
Author(s):  
Mayilvahanan Alagan Chella ◽  
Hans Bihs ◽  
Arun Kamath ◽  
Dag Myrhaug ◽  
Øivind Asgeir Arnsten
Keyword(s):  
Experimental Data ◽  
Free Surface ◽  
Numerical Model ◽  
Numerical Modelling ◽  
Wave Interaction ◽  
Wave Force ◽  
Wave Forces ◽  
Breaking Wave ◽  
Square Configuration ◽  
Breaking Wave Forces

The main purpose of the study is to investigate the breaking wave interaction with a group of four circular cylinders. The physical process of wave breaking involves many parameters and an accurate numerical modelling of breaking waves and the interaction with a structure remain a challenge. In the present study, the open-source (Computational Fluid Dynamics) CFD model REEF3D is used to simulate the breaking wave interaction with the multiple cylinders. The numerical model is based on the incompressible Reynolds Averaged Navier-Stokes (RANS) equations, the level set method for the free surface and the k–ω model for turbulence. The model uses a 5th-order conservative finite difference WENO scheme for the convective discretization and a 3rd-order Runge-Kutta scheme for time discretization. The numerical model is validated with experimental data of large-scale experiments for the free surface elevation and the breaking wave force on a single cylinder. A good agreement is seen between the numerical results and experimental data. Two different configurations with four cylinders are examined: in-line square configuration and diamond square configuration. The breaking wave forces on each cylinder in the group are computed for the two cases and the results are compared with the breaking wave force on a single isolated cylinder. Further, the study investigates the water surface elevations and the free surface flow features around the cylinders. In general, the cylinders in both configurations experience the maximum forces lower than the maximum force on a single cylinder. The results of the present study show that the interference effects from the neighbouring cylinders in a group strongly influence the kinematics around and the breaking wave forces on them.

Structural Analysis of a Hybrid Substructure With Multi-Cylinder for 5MW Offshore Wind Turbines

2014 ◽  
Author(s):  
Min-Su Park ◽  
Youn-Ju Jeong ◽  
Young-Jun You
Keyword(s):  
Free Surface ◽  
Structural Analysis ◽  
Wind Turbine ◽  
Wind Turbines ◽  
Expansion Method ◽  
Wave Force ◽  
Offshore Wind ◽  
Wave Forces ◽  
Offshore Wind Turbines ◽  
Scattering Wave

The substructure for offshore wind turbines is strongly influenced by the effect of wave forces as the size of substructure increases. Therefore, it is very important to reduce the wave force acting on substructures. In the present study the hybrid substructure, which is composed of a multi-cylinder having different radius near free surface and a gravity substructure at the bottom of multi-cylinder, is suggested to reduce the wave forces. The fluid domain is divided into two regions to calculate the wave forces acting on the hybrid substructure with multi-cylinder and the scattering wave in each fluid region is expressed by an Eigen-function expansion method. The comparison between the mono pile and the hybrid substructure is made for wave forces. Using the wave forces obtained from this study, the structural analysis of hybrid substructure is carried out through ANSYS mechanical. In order to investigate the resonance between the wind turbine and the hybrid substructure, the modal analysis is also carried out.

EFFECTS OF SURFACE TENSION ON TRAPPED MODES IN A TWO-LAYER FLUID

2015 ◽  
Vol 57 (2) ◽  
pp. 189-203 ◽  
Author(s):  
S. SAHA ◽  
S. N. BORA
Keyword(s):  
Surface Tension ◽  
Free Surface ◽  
Circular Cylinder ◽  
Boundary Value Problems ◽  
Finite Depth ◽  
Trapped Modes ◽  
Trapped Waves ◽  
Linearized Theory ◽  
Horizontal Circular Cylinder ◽  
Effect Of Surface

We consider a two-layer fluid of finite depth with a free surface and, in particular, the surface tension at the free surface and the interface. The usual assumptions of a linearized theory are considered. The objective of this work is to analyse the effect of surface tension on trapped modes, when a horizontal circular cylinder is submerged in either of the layers of a two-layer fluid. By setting up boundary value problems for both of the layers, we find the frequencies for which trapped waves exist. Then, we numerically analyse the effect of variation of surface tension parameters on the trapped modes, and conclude that realistic changes in surface tension do not have a significant effect on the frequencies of these.

Boundary Layer Measurements at an Internal Free Surface in a Partially Filled Horizontal and Rapidly-Rotating Container

1989 ◽  
Vol 111 (4) ◽  
pp. 457-463 ◽  
Author(s):  
T. J. Singler
Keyword(s):  
Boundary Layer ◽  
Free Surface ◽  
Circular Cylinder ◽  
Steady Flow ◽  
Symmetry Axis ◽  
Azimuthal Velocity ◽  
Free Surfaces ◽  
Horizontal Circular Cylinder ◽  
Good Agreement

Steady flow in a partially filled horizontal circular cylinder rotating rapidly about its symmetry axis is investigated experimentally. Radial boundary layer profiles of the azimuthal velocity in the neighborhood of the internal free surface are reported for a range of inverse Froude numbers and for two types of free surfaces. Results indicate good agreement with an existing theory.

Analysis of a FOWT Model in Bichromatic Waves: An Investigation on the Effect of Combined Wave-Frequency and Slow Motions on the Calibration of Drag and Inertial Force Coefficients

2020 ◽  
Author(s):  
Lucas H. S. do Carmo ◽  
Pedro C. de Mello ◽  
Edgard B. Malta ◽  
Guilherme R. Franzini ◽  
Alexandre N. Simos ◽  
...  
Keyword(s):  
Inertial Force ◽  
Added Mass ◽  
Wave Frequency ◽  
Offshore Wind ◽  
Forced Oscillations ◽  
Wave Flow ◽  
Complex Flow ◽  
Force Coefficients ◽  
Floating Offshore Wind Turbines ◽  
Periodic Components

Abstract The choice of drag and inertia coefficients are critical for the evaluation of hydrodynamic loads in slender cylinders using either Morison’s equation or an approach where viscous forces are simply added to the results of potential theory. Many studies available in the literature have considered fixed cylinders under the action of (two dimensional) sinusoidal currents, showing that the average values of drag and added mass coefficients can be correlated with the Keulegan-Carpenter and Reynolds numbers. However, when the semi-empirical models are used for the analysis of Floating Offshore Wind Turbines (FOWTs), many other aspects of the flow may play an important role, such as the spatial variations of the wave flow over the hull, three-dimensional flow effects associated with the floater motions, the presence of heave plates, among others. The present work is based on a case-study involving a simplified version of the floater of a semi-submersible FOWT and deals with cases where the incoming flow is composed of more than one frequency and body motions are a combination of periodic components with very different frequencies (wave frequency and slow-drift motions). In this case, the choice of proper coefficients for the Morison’s approach becomes somewhat puzzling, to say the least. The objective is to understand how the more complex flow and the coexistence of different frequencies affect the hydrodynamic forces and whether proper values of force coefficients can indeed be obtained from simplified model tests performed in the absence of incoming waves, such as forced oscillations and decay tests. For doing so, the paper analyses the results of an experimental campaign performed with the model scale floater (1:80) composed of four vertical circular columns. Three sets of tests are taken into account: forced oscillations of the hull, free decays of the moored model, and motions under the action of waves (monochromatic and bichromatic). The first two are used to assess the values of added mass and drag coefficients (and also for obtaining linearized damping levels), while the third group of tests helps to evaluate the accuracy of the motions predicted when using these coefficients in frequency-domain computations.

Breaking Wave Interaction With a Group of Four Vertical Slender Cylinders in Two Square Arrangements

2019 ◽  
Vol 141 (6) ◽  
Author(s):  
Mayilvahanan Alagan Chella ◽  
Hans Bihs ◽  
Arun Kamath ◽  
Dag Myrhaug ◽  
Øivind Asgeir Arntsen
Keyword(s):  
Experimental Data ◽  
Free Surface ◽  
Numerical Model ◽  
Wave Interaction ◽  
Wave Force ◽  
Maximum Force ◽  
Wave Forces ◽  
Breaking Wave ◽  
Square Configuration ◽  
Breaking Wave Forces

The main purpose of the study is to investigate the breaking wave interaction with a group of four circular cylinders. The physical process of wave breaking involves many parameters, and an accurate numerical modeling of breaking waves and the interaction with a structure remain a challenge. In the present study, the open-source computational fluid dynamics (CFD) model REEF3D is used to simulate the breaking wave interaction with multiple cylinders. The numerical model is based on the incompressible Reynolds-averaged Navier–Stokes (RANS) equations, the level set method for the free surface, and the k–ω model for turbulence. The numerical model is validated with experimental data of large-scale experiments for the free surface elevation and the breaking wave force on a single cylinder. A good agreement is obtained between the numerical results and experimental data. Two different configurations with four cylinders are examined: in-line square configuration and diamond square configuration. For both configurations, three different tank widths and four different spacings between the cylinders are investigated. The breaking wave forces on each cylinder in the group are computed for each case for the two configurations, and the results are compared with the breaking wave force on a single isolated cylinder. Furthermore, the study investigates the water surface elevations and the free surface flow features around the cylinders. For the closely spaced cylinders in a relatively narrower tank, the cylinders in both configurations experience the maximum forces lower than the maximum force on a single cylinder. But for the widely spaced cylinder in a relatively wider tank, the forces are higher and lower for the upstream cylinders and downstream cylinders, respectively, than the maximum force on a single isolated cylinder. The results of the present study show that the interference effects from the neighboring cylinders in a group strongly influence the kinematics around and the breaking wave forces on them.

scholarly journals Numerical Simulation of Breaking Wave Loading on Standing Circular Cylinders with Different Transverse Inclined Angles

2020 ◽  
Vol 10 (4) ◽  
pp. 1347
Author(s):  
Sen Qu ◽  
Shengnan Liu ◽  
Muk Chen Ong ◽  
Shuzheng Sun ◽  
Huilong Ren
Keyword(s):  
Experimental Data ◽  
Vertical Cylinder ◽  
Wave Force ◽  
High Order ◽  
Numerical Results ◽  
Circular Cylinders ◽  
Wave Forces ◽  
Breaking Wave ◽  
Time Step ◽  
Inclined Angle

The purpose of this paper is to numerically simulate the breaking wave past a standing cylinder with different transverse inclined angles. The numerical simulations are carried out by solving the Unsteady Reynolds-Averaged Navier–Stokes (URANS) equations with the k − ω S S T turbulence model. The air–water interface is captured using the Volume of Fluid (VOF) method. The convergence studies on the grid and time-step are performed by examining the total horizontal breaking wave forces on the vertical cylinder. The present numerical results have been validated with the published experimental data. A good agreement is obtained between the present numerical results and the experimental data in terms of the surface elevation and the horizontal breaking wave force. Moreover, the total horizontal breaking wave force is decomposed into low-order and high-order wave forces through Fast Fourier Transform (FFT). It is observed that the free surface elevations in front of the cylinder and the normalized high-order wave force have a minimum value when the transverse inclined angle of the cylinder is 45°. The secondary load causing the higher-harmonic ringing motion of structures is not observed when the cylinder is placed with the transverse inclined angles of 30° and 45°.

Numerical Simulation of Nonlinear Wave Diffraction by a Vertical Cylinder

1992 ◽  
Vol 114 (1) ◽  
pp. 36-44 ◽  
Author(s):  
C. Yang ◽  
R. C. Ertekin
Keyword(s):  
Experimental Data ◽  
Circular Cylinder ◽  
Nonlinear Wave ◽  
Wave Diffraction ◽  
Three Dimensional ◽  
Vertical Cylinder ◽  
Radiation Condition ◽  
Wave Force ◽  
Second Order ◽  
Time Stepping

A three-dimensional time domain approach is used to study nonlinear wave diffraction by a fixed, vertical circular-cylinder that extends to the sea floor. In this approach, the development of the flow can be obtained by a time-stepping procedure, in which the velocity potential of the flow at any instant of time is obtained by the boundary-element method. In the numerical calculations, the exact body-boundary condition is satisfied on the instantaneous wetted surface of the cylinder, and an extended Sommerfeld condition is developed and used as the numerical radiation condition. The fourth-order Adams-Bashford method is employed in the time stepping scheme. Calculations are done to obtain the nonlinear diffraction of solitary waves and Stokes second-order waves by a vertical circular-cylinder. Numerical results are compared with the available linear and second-order wave-force predictions for some given wave height and wavelength conditions, and also with experimental data. Present horizontal force results agree better with the experimental data than the previous predictions.

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